One of the most ancient brain circuits in evolutionary terms, it is involved in motor control, posture and gait and in the fluid execution of complex sequences of motor movements. Or consider the cerebellum, the “little brain” underneath the back of the brain. Yet these tetraplegics continue to experience life in all its variety-they see, hear, smell, feel emotions and remember as much as before the incident that radically changed their life. If the spinal cord is completely severed by trauma to the neck region, victims are paralyzed in legs, arms and torso, unable to control their bowel and bladder, and without bodily sensations. Take the spinal cord, a foot-and-a-half-long flexible tube of nervous tissue inside the backbone with about a billion nerve cells. But the seat of consciousness can be further ring-fenced. The brain as a whole can be considered an NCC, after all: it generates experience, day in and day out. When defining the NCC, the qualifier “minimal” is important. What must happen in your brain for you to experience a toothache, for example? Must some nerve cells vibrate at some magical frequency? Do some special “consciousness neurons” have to be activated? In which brain regions would these cells be located? We seek, in particular, the neuronal correlates of consciousness (NCC), defined as the minimal neuronal mechanisms jointly sufficient for any specific conscious experience. What is it about a highly excitable piece of brain matter that gives rise to consciousness? Once we can understand that, we hope to get closer to solving the more fundamental problem. More than a quarter of a century ago Francis Crick and I decided to set aside philosophical discussions on consciousness (which have engaged scholars since at least the time of Aristotle) and instead search for its physical footprints.
The majority of scholars accept consciousness as a given and seek to understand its relationship to the objective world described by science. As I have very little sympathy for this desperate solution to the mind-body problem, I shall move on. If I have a tooth abscess, however, a sophisticated argument to persuade me that my pain is delusional will not lessen its torment one iota. All I would need to explain is why you, I and most everybody else is so convinced that we have feelings at all. If that assertion was true, this essay would be very short. That is, they either deny that qualia exist or argue that they can never be meaningfully studied by science. Many modern analytic philosophers of mind, most prominently perhaps Daniel Dennett of Tufts University, find the existence of consciousness such an intolerable affront to what they believe should be a meaningless universe of matter and the void that they declare it to be an illusion. The origin and nature of these experiences, sometimes referred to as qualia, have been a mystery from the earliest days of antiquity right up to the present. It is the tune stuck in your head, the sweetness of chocolate mousse, the throbbing pain of a toothache, the fierce love for your child and the bitter knowledge that eventually all feelings will end. Consciousness is everything you experience.